Solid state imagers, such as an x-ray imager typically include a photosensor array coupled to a scintillating medium. Radiation absorbed in the scintillator generates optical photons which in turn pass into a photosensor, such as a photodiode, in which the optical photon is absorbed and an electrical signal corresponding to the incident optical photon flux is generated. Substantially hydrogenated amorphous silicon (a-Si) is commonly used in the fabrication of photosensors due to the advantageous photoelectric characteristics of a-Si and the relative ease of fabricating such devices. In particular, photosensitive elements, such as photodiodes, can be formed in connection with necessary control or switching elements, such as thin film transistors (TFT's), in a relatively large array. The fabrication of such arrays is facilitated by the use of a-Si, which is used in the formation of both the TFT's and the photodiodes. Fabrication of the array is also facilitated by the deposition of a scintillator material directly over the photosensor array, but care must be taken to both protect the components of the photosensor array and ensure structural integrity of the scintillator/photosensor array assembly.
The performance of amorphous silicon based imagers can be degraded by a number of factors, including, for example, exposure to moisture (which can cause the leakage of a-Si photodiodes to increase irreversibly), exposure to materials, such as solvents used in the fabrication process, that degrade the electrical characteristics of the a-Si photodiode or may damage the polymeric dielectric materials, or by exposure to temperatures higher than those of the a-Si deposition processes (e.g., greater than about 250.degree. C.). It is thus beneficial to provide a protective boundary for a-Si components to minimize degradation both in fabrication and during operation of the imager. A protective boundary disposed between the a-Si components of the photosensor array and the scintillator in an imager desirably provides 1) protection of the photosensor array from contamination by the scintillating medium (and vice versa); 2) a surface to which the scintillator material can adhere well; 3) good optical coupling between the scintillator and the underlying pixels in the imager array (that is, a high degree of transmission of the optical photons with a minimum of scattering of the photons); and, 4) a good environmental barrier to protect the photosensor array, especially from moisture.
Direct application of the scintillator material to the upper surface of the photosensor array, (either the common electrode or the barrier layer, if any, deposited to protect the array components) is the most efficient means of fabricating the imager assembly. In most imager devices, it is desirable to ensure a high degree of structural integrity between the scintillator and the upper surface of the photosensor array.
It thus an object of this invention to provide a method of fabricating an imager that provides for a robust structure having strong adhesion between the scintillator and the barrier layer.
It is a further object of this invention to provide a method of treating a barrier layer to improve adhesion to an overlying scintillator layer in a process that does not substantially adversely effect other exposed component materials in the array.